Information Series 134

Information Series 134

Outreach Maps Generated from Remote Sensing Data

This publication includes four maps: the Alberta Geology map, the Alberta Topography map and the satellite images of Edmonton and Calgary.

These maps were created for Alberta Geological Survey (AGS) outreach activities using satellite images and an Alberta geological map. The satellite images used include a Landsat image, an Indian Remote-sensing satellite (IRS) image and a Shuttle Radar Topography Mission (SRTM) image. These images were generated by satellite sensors mounted on these satellites. Satellite sensors act like our eyes; we see colour because our eyes detect the light and our brains process the information into separate colours. The light we see is actually electromagnetic radiation consisting of an electrical field that varies in magnitude in a direction perpendicular to the direction the radiation is travelling, and a magnetic field oriented at right angles to the electrical field. Both these fields travel at the speed of light. A wide range of electromagnetic radiation exists, and the light we see with our eyes belongs to only the visible range of electromagnetic spectrum. The electromagnetic spectrum ranges from the shorter wavelengths (including gamma and x-rays) to the longer wavelengths (including microwaves and broadcast radio waves). Like our eyes, satellite sensors use certain narrow ranges of wavelength to generate images of the Earth. The information from a narrow wavelength range is gathered and stored in a channel, sometimes referred to as a one-band image. We can combine and display channels of information digitally using the three primary colours (blue, green and red). The data from each channel are represented as one of the primary colours, and depending on the relative brightness (i.e., the digital value) of each pixel in each channel, the primary colours combine in different proportions to represent different colours. When we display more than one channel each as a different primary colour, then the brightness levels may be different for each channel/primary colour combination, and they will combine to form a colour image.

Both the Landsat and the IRS satellite use the visible and reflected infrared portion of the electromagnetic spectrum for acquiring images and are called optical sensors. The IRS image used here is a one-band grey image and has a resolution of 5.8 metres. The Landsat image used here is a three-band colour image and was sharpened to a resolution of 15 metres. It shows the natural colour of Alberta in summer. The SRTM sensor uses a different portion of the electromagnetic spectrum; i.e., the microwave. In addition to obtaining the picture of the Earth using microwave spectra, engineers applied Interferometric Synthetic Aperture Radar (InSAR) to acquire elevation information about the Earth's surface. The SRTM image used here is from the topographic data or digital elevation model (DEM) and shows the topography of Alberta.

The Alberta geology used is a simplified version of Alberta Geological Map 236, which is created through collective contribution of AGS geologists.

During creation of the Alberta topography and Edmonton and Calgary maps, the Landsat image was sharpened with the IRS image to obtain an image with the natural summer colour and a high resolution of 5.8 metres. Then, the sharpened image was fused with a sunshade relief image of SRTM DEM to obtain a stereo effect. The Alberta Geology map is created by fusing the SRTM DEM data with the geological map of Alberta to obtain an image with both the topography and geology.